SANAA, Yemen -- The word came in May 2006: Ali Mohammed Nasser Mohammed, a slight, 24-year-old Yemeni with curly black hair and a wispy beard, would be freed from Guantanamo after more than four years. He got a checkup. His photo was taken, as were his fingerprints. He was measured for clothes and shoes, then offered a meeting with the Red Cross.

As the Pentagon tersely put it later in an e-mail to his attorneys: "Your client has been approved to leave Guantanamo."

In the legal netherworld that the U.S. military detention center at Guantanamo Bay, Cuba, has represented since it was opened in 2002, Mohammed, once a cook for the Taliban in Afghanistan, remains stuck in a limbo of mistaken identities, bureaucratic inertia and official neglect. In the eyes of his lawyers, the young Yemeni's case is an indictment of a system, still cloaked in the strictest secrecy and largely beyond accountability, in which a man who faces no charge and no sentence remains deprived of the freedom he was granted more than a year ago.

"It's a lovely illustration of what happens when there's no oversight of the jailer," said a rueful Rayner.

Just before he was to depart on May 18 of last year, on a flight that carried 15 Saudis home, Mohammed was left off the plane for a simple reason: The Saudi government said he was not Saudi, even though he was born there. Under Yemeni and Saudi law, he is Yemeni, by virtue of his parents' citizenship. He carries a Yemeni passport, grew up in Yemen and went to school in Sanaa, the capital, where his parents live.

But his attorneys say the U.S. military still classifies him as Saudi. The Saudi government considers its role over. The Yemeni government says it is unaware of his case. And Mohammed waits, now confined to Guantanamo's newest facility, Camp Six, a maximum-security building with no communal area and no way to talk to other detainees save a shout through a locked door.

"This is a legal issue that has to be looked at," Yemeni Foreign Minister Abu Bakr al-Qirbi said in an interview.

Asked if he was familiar with the case, he replied, "Not really."

A Pentagon spokesman declined to comment specifically on Mohammed's case but said that determining a detainee's citizenship can be "more complex in some parts of the world."

"We use the best information available and work closely with foreign governments to ascertain a detainee's citizenship and nationality," the spokesman, Cmdr. J.D. Gordon, said in a statement.

For lawyers, Mohammed's case is perhaps the most vexing among those of the 100 or so Yemenis who now constitute the single largest group of detainees at Guantanamo. In addition to Mohammed, lawyers say, at least six other Yemenis, and perhaps many more, were cleared for release as long ago as February 2006 but remain imprisoned there.

At least publicly, the Yemeni government insists it wants the men repatriated. Many of them are now entering their sixth year of detention.

"Right from the very onset, Yemen has demanded the release of its citizens and their handing over to the government of Yemen," said Qirbi, who was appointed foreign minister in April 2001. "We have not refused any of our detainees."

Both Qirbi and Western diplomats agree that an arrangement has been in place for their return since at least last summer. A Western diplomat, speaking on condition of anonymity, called the negotiations, which lasted more than a year, "long and difficult."

Under the eventual agreement, the diplomat said, Yemen agreed to keep the United States informed of the released detainees' fate and offered assurances that they would not leave the country for places such as Iraq or Afghanistan. Qirbi said Yemen has insisted that there be no conditions -- anything else would constitute a violation of sovereignty -- but Yemeni officials appear to have complied informally.

The diplomat said he expected another group of Yemenis to be released "within a month or so."

The U.S. military has reduced by almost half the number of prisoners at Guantanamo since the peak of 680 in May 2003. Of the roughly 385 still there, U.S. officials say they intend to put 60 to 80 on trial. So far, lawyers say, all the European detainees have been returned, along with two Australians. Half the Afghan detainees have gone home and nearly half of the Saudis. But the United States has repatriated only eight Yemeni citizens, six of them in December.

Qirbi blamed the delays on new U.S. procedures at Guantanamo and the intervention of the detainees' attorneys in the cases, contentions the lawyers contest. The Western diplomat said the delays, in part, reflected a desire by U.S. officials to monitor what became of the most recent returnees.

Despite the insistence of Qirbi and other Yemeni officials, the diplomat also echoed the contention of Yemeni and American lawyers that the Yemeni government has exerted little pressure to bring the men home, and diplomats acknowledged that the government, in particular President Ali Abdullah Saleh, was initially reluctant to see the men return.

"It's not an issue we get hammered on every day," the diplomat said.

Mohammed Naji Allaw, a lawyer and the coordinator of the Sanaa-based National Organization for Defending Rights and Freedoms, which has advocated on behalf of the detainees, was more blunt. "They don't care," he said of government officials here. "They say, 'Bring them home, don't bring them, it doesn't really matter.' "

Born in Jiddah, Mohammed came to Yemen as a small child, attending high school in Sanaa. At 18, he went to Afghanistan. Mohammed has acknowledged attending a training camp there, but said he spent nearly all his time as a cook and guard behind the lines in Bagram. After the U.S.-led invasion in October 2001, his attorneys said, he fled to Pakistan, where he was captured and turned over to the U.S. military.

Unclassified transcripts of his interviews with military officials at Guantanamo paint a portrait of a young man still coming of age, at times baffled by the military's black-and-white views of what constitutes a threat. He refused to make a statement under oath unless they first agreed to release him. When officials asked whether he was a frontline fighter carrying an AK-47, he grew confused at the designation. "What is 47?" he asked. "I know Kalashnikov, but I do not know what you mean by 47."

At another point, he disputed an allegation that he sang a song at Guantanamo praising Osama bin Laden. "I don't have the voice to sing or to say anything in melody," he said.

Rayner and her colleague, Ramzi Kassem, both law professors at the Fordham University School of Law in New York, first visited Mohammed in November, more than four years after the Yemeni entered Guantanamo. They said he was almost casual about his predicament.

"He said, 'I'm meeting with you guys but I don't think all this is necessary. I've been approved for release,' " Kassem said.

By the time of a meeting in January, he had grown more worried. By March, nearly a month after the lawyers themselves were notified in an e-mail from the U.S. military that Mohammed had been approved to leave Guantanamo, he was becoming desperate, they said. Rayner, in particular, was worried about an almost incidental request: Mohammed insisted on breaking for lunch because his favorite dish -- macaroni and chicken -- was being served. To Rayner, the request was a sign that he was becoming institutionalized.

"The routine had become so ingrained it was hard to break out of," she said.

Rayner and Kassem arrived here with a dozen other lawyers in May to press Yemen's government on the cases of Mohammed and other detainees already cleared for release. They requested -- and were refused -- meetings with Saleh, the heads of political and national security and the interior minister. They saw only the foreign minister and the human rights minister.

At the meeting with Qirbi, the lawyers said, the foreign minister asked them to provide him information on the cases.

"Once we have the information, we'll obviously have to raise it with the Americans," he said in the interview.

Qirbi meant the request as a gesture of cooperation. But Allaw, the human rights lawyer, saw it as emblematic of the problem. In his 11th-floor office in a bank building in Sanaa, photocopied papers of Mohammed's case were spread on a desk -- his parents' identification cards, marriage certificates and education records.

"If someone doesn't even know the names and exact number of detainees, how can they pressure another government?" asked the bearded Allaw, his tone a little jaded. "That's the most basic of information, and they're requesting it from us."